That's a long way for that rod, I don't care how good you are. And in trout water? Once you've got 75 feet out there you have to control it which is a heck of a lot mending with a short rod. Maybe wade closer? In all seriousness I rarely throw that far with a ten weight in the salt unless its real skinny water, I just move the boat closer.
I guess step one is to go to the park. Practice cast as far as you can reasonably control the line (and I'm talking consistently, not one cast out of ten).
Then thrown in a mid air mend or two. That is your maximum range.
Now, do you really need more? Someone suggested shooting heads, I hate them, but they work for distance, but on a 5wt?
One option is to overline it a bit and get a six weight line in a bonefish taper or the like.
Or get a longer and faster rod, a 9'-10' Sage or Orvis or Loomis in one of their superfast models. Or even move up to a six weight geared for bass or the salt like a Sage RPL, but it will less fun to fight average size trout.
That's about all the suggestions I have, but I'm sticking with getting closer as option one and getting a longer and faster rod as option two if your casting isn't the problem, 75 feet is a long way for a 5wt 8'6" rod.